Varainductor having ground and floating planes and method of using

ABSTRACT

A varainductor includes a signal line over a substrate. The varainductor further includes a first ground plane over the substrate. The varainductor further includes a first floating plane over the substrate, wherein the first floating plane is between the first ground plane and the signal line, and the first floating plane is a same distance from the substrate as the first ground plane. The varainductor further includes a first transistor configured to selectively electrically connect the first ground plane to the first floating plane. The varainductor further includes a second transistor configured to selectively electrically connect the first ground plane to the first floating plane, wherein a gate of the first transistor is connected to a gate of the second transistor.

PRIORITY CLAIM

The present application is a continuation of U.S. application Ser. No.15/950,585, filed Apr. 11, 2018, which is a continuation of U.S.application Ser. No. 13/837,184, filed Mar. 15, 2013, now U.S. Pat. No.9,954,488, issued on Apr. 24, 2018, which are incorporated herein byreference in their entireties.

BACKGROUND

A phase locked loop (PLL) is a control system configured to generate anoutput signal whose phase is related to a phase of a reference signal.PLLs are used in demodulator systems, tone detectors, and frequencysynthesizers. PLLs are also used in digital applications which include ahigh frequency period signal to synchronize events within a circuit.

PLLs include a voltage controlled oscillator (VCO) configured to adjusta frequency of the output signal based on a control signal. In someinstances, the VCO includes a varactor. A varactor is a diode having avariable capacitance. In some instances, a metal-oxide-semiconductor(MOS) varactor is used in the VCO. A transmission-line-based inductor isalso included in the VCO for high frequency applications, e.g.,millimeter-wave region, in some instances.

A Q factor is a measure of an amount of energy loss relative to theenergy stored in a resonator, such as the varactor. As the Q factordecreases, the oscillations in the varactor are damped more quickly. Insome instances, if the Q factor is too low, the varactor cannot initiateoscillation in the VCO, which inhibits the PLL from locking the outputsignal to the reference signal. As a frequency of the reference signalincreases, the Q factor of the MOS varactor decreases. This decreasepotentially prevents initiation of oscillation in high frequencyapplications.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments are illustrated by way of example, and not bylimitation, in the figures of the accompanying drawings, whereinelements having the same reference numeral designations represent likeelements throughout. It is emphasized that, in accordance with standardpractice in the industry various features may not be drawn to scale andare used for illustration purposes only. In fact, the dimensions of thevarious features in the drawings may be arbitrarily increased or reducedfor clarity of discussion.

FIG. 1 is a perspective view of a varainductor in accordance with one ormore embodiments;

FIG. 2 is a top view of a varainductor in accordance with one or moreembodiments;

FIG. 3 is a perspective view of a varainductor in accordance with one ormore embodiments;

FIG. 4 is a perspective view of a varainductor in accordance with one ormore embodiments;

FIG. 5 is a schematic diagram of a voltage controlled oscillatorincluding a varainductor in accordance with one or more embodiments;

FIG. 6 is a schematic functional diagram of a phase locked loopincluding a varainductor in accordance with one or more embodiments;

FIG. 7 is a flow chart for method of designing a varainductor inaccordance with one or more embodiments;

FIG. 8 is a flow chart for a method of operating a varainductor inaccordance with one or more embodiments; and

FIG. 9 is a flow chart for a method of operating a phase locked loopincluding a varainductor in accordance with one or more embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are examples and are not intended to belimiting.

FIG. 1 is a perspective view of a varainductor 100 in accordance withone or more embodiments. Varainductor 100 includes a substrate 102 and asignal line 104 disposed over the substrate and extending in a firstdirection. Signal line 104 is configured to receive a DC operatingvoltage and signal. A pair of floating planes 106 is disposed oversubstrate 102 and extends in the first direction parallel to signal line104. Each of the pair of floating planes 106 is configured to beelectrically floating. One of the pair of floating planes 106 isdisposed on each side of signal line 104. A pair of ground planes 108 isdisposed over substrate 102 and extends in the first direction parallelto signal line 104. Each of the pair of ground planes 108 is configuredto receive a ground or reference voltage. One of the pair of groundplanes 108 is disposed on each side of signal line 104 with one of thepair of floating planes 106 positioned between the signal line and theground plane. An array of switches 110 is disposed over substrate 102and is capable of electrically connecting one of the pair of groundplanes 108 with a respective one of the pair of floating planes 106.Varainductor 100 is configured to receive a switch control signal Vtune,which is electrically connected to array of switches 110. Switch controlsignal Vtune determines a level of electrical connectivity betweenground plane 108 and the respective floating plane 106, to adjust aninductance level of varainductor 100. A dielectric material (not shown)is disposed between substrate 102, signal line 104, floating planes 106and ground planes 108.

In some embodiments, substrate 102 comprises an elementary semiconductorincluding silicon or germanium in crystal, polycrystalline, or anamorphous structure; a compound semiconductor including silicon carbide,gallium arsenic, gallium phosphide, indium phosphide, indium arsenide,and indium antimonide; an alloy semiconductor including SiGe, GaAsP,AlInAs, AlGaAs, GaInAs, GaInP, and GaInAsP; any other suitable material;or combinations thereof. In some embodiments, the alloy semiconductorsubstrate has a gradient SiGe feature in which the Si and Ge compositionchange from one ratio at one location to another ratio at anotherlocation of the gradient SiGe feature. In some embodiments, the alloySiGe is formed over a silicon substrate. In some embodiments, substrate102 is a strained SiGe substrate. In some embodiments, the semiconductorsubstrate has a semiconductor on insulator structure, such as a siliconon insulator (SOI) structure. In some embodiments, the semiconductorsubstrate includes a doped epi layer or a buried layer. In someembodiments, the compound semiconductor substrate has a multilayerstructure, or the substrate includes a multilayer compound semiconductorstructure.

Signal line 104 comprises a conductive material. In some embodiments,signal line 104 comprises copper, aluminum, tungsten, polysilicon, aconductive polymer, other suitable conductive materials, or combinationstherefore. Signal line 104 is configured to receive the DC operatingvoltage and signal of varainductor 100. In some embodiments,varainductor 100 is used in a voltage controlled oscillator (VCO) of aphase locked loop (PLL). Signal line 104 has a length L in the firstdirection. In some embodiments, the length L ranges from about 10micrometers (μm) to about 300 μm. As the length L of signal line 104increases, a total inductance of varainductor 100 also increases. Signalline 104 has a width Ws in a second direction perpendicular to the firstdirection. In some embodiments, the width Ws ranges from about 2 μm toabout 6 μm. As the width Ws of signal line 104 increases, acharacteristic impedance of varainductor 100 decreases. Thecharacteristic impedance is a ratio of a voltage and a current travelingalong a transmission line. Characteristic impedance is directly relatedto the total inductance of varainductor 100.

Each floating plane 106 comprises a conductive material. In someembodiments, each floating plane 106 comprises copper, aluminum,tungsten, polysilicon, a conductive polymer, other suitable conductivematerials, or combinations therefore. In some embodiments, each floatingplane 106 comprises a same material as signal line 104. In someembodiments, at least one floating plane 106 comprises a differentmaterial from signal line 104. Each floating plane 106 has a length L inthe first direction. In some embodiments, the length L ranges from about10 micrometers (μm) to about 300 μm. The length L of the floating planes106 is substantially equal to the length L of signal line 104. Eachfloating plane 106 has a width W1 in the second direction. In someembodiments, the width W1 ranges from about 2 μm to about 30 μm. As thewidth W1 of floating planes 106 increases, a grounding capability ofvarainductor 100 increases, which increases the Q factor of thevarainductor. In some embodiments, the width W1 of floating planes 106is the same as the width Ws of signal line 104. In some embodiments, thewidth W1 of floating planes 106 is different from the width Ws of signalline 104. Floating planes 106 are spaced from signal line 104 in thesecond direction by a first spacing distance S1. In some embodiments,the first spacing distance S1 ranges from about 2 μm to about 30 μm. Asthe first spacing distance S1 between floating planes 106 and signalline 104 increases, the characteristic impedance increases.

Each ground plane 108 comprises a conductive material. In someembodiments, each ground plane 108 comprises copper, aluminum, tungsten,polysilicon, a conductive polymer, other suitable conductive materials,or combinations therefore. In some embodiments, each ground plane 108comprises a same material as signal line 104 or floating planes 106. Insome embodiments, at least one ground plane 108 comprises a differentmaterial from signal line 104 or floating planes 106. Each ground plane108 has a length L in the first direction. In some embodiments, thelength L ranges from about 10 micrometers (μm) to about 300 μm. Thelength L of the ground planes 108 is substantially equal to the lengthof signal line 104. Each ground plane 108 has a width W2 in the seconddirection. In some embodiments, the width W2 ranges from about 4 μm toabout 30 μm. As the width W2 of ground planes 108 increases, a groundingcapability of varainductor 100 increases, which increases the Q factorof the varainductor. In some embodiments, the width W2 of ground planes108 is the same as the width Ws of signal line 104 or the width W1 offloating planes 106. In some embodiments, the width W2 of ground planes108 is different from the width Ws of signal line 104 or the width W1 offloating planes 106. Ground planes 108 are spaced from adjacent floatingplanes 106 in the second direction by a second spacing distance S2. Insome embodiments, the second spacing distance S2 ranges from about 2 μmto about 30 μm. As the second spacing distance S2 between floatingplanes 106 and ground planes 108 increases, a tuning range ofvarainductor 100 is increased. In some embodiments, the first spacingdistance S1 is equal to the second spacing distance S2. In someembodiments, the first spacing distance S1 is different from the secondspacing distance S2.

Array of switches 110 comprises an array of switching elementsconfigured to selectively connect ground plane 108 to a respectivefloating plane 106. In some embodiments, the switching elements comprisetransistors, thyristors, micro-electromechanical systems (MEMS), orother suitable switching elements. Each switch of the array of switches110 is configured to receive switch control signal Vtune. In someembodiments, array of switches 110 is configured to increase electricalconnectivity between floating plane 106 and ground plane 108 as avoltage level of switch control signal Vtune increases. In someembodiments, array of switches 110 is configured to increase electricalconnectivity between floating plane 106 and ground plane 108 as thevoltage level of switch control signal Vtune decreases. In someembodiments, array of switches 110 is configured to gradually adjustelectrical connectivity between floating plane 106 and ground plane 108as the voltage level of switch control signal Vtune changes. In someembodiments, array of switches 110 is configured to adjust electricalconnectivity between floating plane 106 and ground plane 108 in adigital manner as the voltage level of switch control signal Vtunechanges.

The dielectric material is disposed between the various elements ofvarainductor 100. The dielectric material is configured to provideelectrical insulation between signal line 104, floating planes 106 andground planes 108. In some embodiments, the dielectric material is alow-k dielectric material. In some embodiments, the dielectric materialhas a k value less than 3.5. In some embodiments, the dielectricmaterial has a k value less than 2.5. Suitable low-k dielectricmaterials include fluorinated silica glass (FSG); carbon doped siliconoxide, BLACK DIAMOND® (Applied Materials of Santa Clara, Calif.),xerogel, aerogel, amorphous fluorinated carbon, parylene,bis-benzocyclobutenes (BCB), SILK® (Dow Chemical, Midland, Mich.),polyimide, porous polymeric materials, other suitable materials orcombinations thereof. In some embodiments, the low-k dielectric materialreduces tuning problems within varainductor 100. In some embodiments,each of signal line 104, floating planes 106 and ground planes 108 areformed in a same plane in the dielectric material. In some embodiments,at least one of signal line 104, floating planes 106 or ground planes108 are formed in a different plane in the dielectric layer from atleast another of the signal line, the floating planes or the groundplanes.

FIG. 2 is a top view of varainductor 100 in accordance with one or moreembodiments. Varainductor 100 includes switches 120 between floatingplane 106 and a respective ground plane 108. Switches 120 are individualswitches from array of switches 110 (FIG. 1). As mentioned above,switches 120 are able to be implemented using a variety of switchingelements including transistors, thyristors, MEMS, or other suitableswitching elements. In some embodiments, every switch 120 hassubstantially the same structure. In some embodiments, at least oneswitch 120 has a different structure than at least one other switch 120.A different structure means a different type of switching element, adifferent dimension, a different threshold voltage, or anotherstructural difference within the switching elements.

Each switch 120 is spaced from an adjacent switch by a switch spacingdistance A. As a resistance between ground plane 108 and floating plane106 decreases, the tuning range of varainductor 100 increases. A largerswitch spacing distance A results in fewer switches 120 between floatingplane 106 and ground plane 108, which in turn increases the resistancebetween the ground plane and the floating plane. To maintain a lowresistance between ground plane 108 and floating plane 106, switchspacing distance A is made as small as design rules and a criticaldimension of production capabilities permit to maximize the tuning rangeof varainductor 100. In some embodiments, for a floating plane 106having a length of approximately 100 μm, sixteen switches are positionedbetween the floating plane and ground plane 108.

FIG. 3 is a perspective view of a varainductor 300 in accordance withone or more embodiments. Varainductor 300 is similar to varainductor100, except array of switches 110 is replaced with array of switches310. Array of switches 310 is configured to facilitate bit control ofthe switches between floating plane 106 and the respective ground plane108. In the embodiment of FIG. 3, each switch of array of switches 310is configured to receive a different control signal to selectivelyactivate/de-activate the switch. In some embodiments, a first group ofswitches of array of switches 310 is configured to receive a firstcontrol signal and a second group of switches of array of switches 310is configured to receive a second control signal different from thefirst control signal. In some embodiments, an external circuit is usedto generate the individual switch control signals for varainductor 300.In some embodiments, at least one switch of the array of switches 310has a different voltage drop across the switch than at least anotherswitch of the array of switches.

Bit control of the electrical connection between ground plane 108 andfloating plane 106 enables varainductor 300 to have a more finelyadjustable capacitance between the ground plane 108 and the floatingplane 106 in comparison with varainductor 100. In some embodiments, bitcontrol facilitates more efficient power consumption because theindividual switch control signals for each switch of array of switches310 has a lower power consumption than switch control signal Vtune ofvarainductor 100.

FIG. 4 is a perspective view of a varainductor 400 in accordance withone or more embodiments. Varainductor 400 is similar to varainductor 100(FIG. 1), except ground planes 108 are replaced with ground planes 108′.Ground planes 108′ differ from ground planes 108 in that ground planes108′ are formed by a stack of conductors in different planes of thedielectric material with the conductors electrically connected to oneanother by vias. Ground planes 108′ distribute a total area of agrounding conductor in three dimensions instead of two dimensions, aswith ground planes 108. The three dimensional distribution reduces anoverall area of varainductor 400 in comparison with varainductor 100.

Varainductor 400 also differs from varainductor 100 in that varainductor400 includes a shielding plane 410 between signal line 104 and substrate102. Shielding plane 410 extends between signal line 104 and substrate102 from one floating plane 106 to the other floating plane 106.Shielding plane 410 is electrically connected to floating planes 106 byvias through the dielectric material. Shielding plane 410 is a slot typeshielding plane where the slots account for approximately 50% of thetotal area under signal line 104. In some embodiments, shielding plate410 includes slots which account for more or less than 50% of the totalarea under signal line 104. In some embodiments, shielding plate 410 isa solid shielding plate with no slots. In some embodiments, shieldingplane 410 does not extend an entire distance from one floating plane 106to the other floating plane 106. In some embodiments, shielding plane410 is electrically separated from at least one of floating planes 106.In some embodiments, shielding plane 410 is a different type ofshielding plane, such as braided shielding structures or other suitableshielding structures. In some embodiments, more than one shielding plane410 is disposed between signal line 104 and substrate 102. In someembodiments, the more than one shielding planes 410 are electricallyconnected to one another by vias through the dielectric material.

Although varainductor 400 is depicted having array of switches 110, oneof ordinary skill in the art would recognize varainductor 400 havingarray of switches 310 is within the scope of this description.

FIG. 5 is a schematic diagram of an oscillator circuit 500 including avarainductor in accordance with one or more embodiments. Oscillatorcircuit 500 includes a first varainductor 502 configured to receive a DCoperating voltage and provide inductance for signal oscillation.Oscillator circuit 500 further includes a second varainductor 504configured to receive a DC operating voltage and provide inductance forsignal oscillation. First varainductor 502 is electrically connected inparallel to second varainductor 504. A current source is disposedbetween first varainductor 502 and the operating voltage VDD and betweensecond varainductor 504 and the operating voltage VDD. Firstvarainductor 502 is connected in series with a first transistor 506. Afirst terminal of first transistor 506 is connected to firstvarainductor 502 and a second terminal of first transistor 506 isconnected to a reference voltage, e.g. ground. Second varainductor 504is connected in series with a second transistor 508. A first terminal ofsecond transistor 508 is connected to second varainductor 504 and asecond terminal of second transistor 508 is connected to the referencevoltage. A gate of first transistor 506 is connected to a first outputnode A between second varainductor 504 and second transistor 508. A gateof second transistor 508 is connected to a second output node B betweenfirst varainductor 502 and first transistor 506. In some embodimentswhere first varainductor 502 and second varainductor 504 have astructure of varainductor 100 (FIG. 1) or varainductor 400 (FIG. 4),oscillator circuit 500 is a voltage controlled oscillator (VCO) In someembodiments where varainductors 502 and 504 have a structure ofvarainductor 300 (FIG. 3), oscillator circuit 500 is a digitallycontrolled oscillator (DCO)

In some embodiments, first varainductor 502 comprises varainductor 100(FIG. 1). In some embodiments, first varainductor 502 comprises avarainductor other than varainductor 100, such as varainductor 300 (FIG.3), varainductor 400 (FIG. 4), or another suitable varainductor. In someembodiments, second varainductor 504 comprises varainductor 100. In someembodiment, second varainductor 504 comprises a varainductor other thanvarainductor 100, such as varainductor 300, varainductor 400, or anothersuitable varainductor. In some embodiments, first varainductor 502 has adifferent structure from second varainductor 504.

In some embodiments, first transistor 506 and second transistor 508 areindependently selected from p-type metal-oxide-semiconductor (PMOS)transistors, n-type metal-oxide-semiconductor (NMOS) transistors, orother suitable transistors.

FIG. 6 is a schematic functional diagram of a phase locked loop (PLL)600 including a varainductor in accordance with one or more embodiments.PLL 600 includes a phase frequency detector (PFD) 602 configured toreceive a reference frequency f_(REF) and a feedback frequency f_(FBK).PFD 602 is configured to determine a difference between referencefrequency f_(REF) and feedback frequency f_(FBK), and output a firstcontrol signal. PLL 600 further includes a charge pump (CP) 604configured to receive the first control signal. CP 604 is configured toconvert the first control signal to an analog voltage signal and outputthe analog voltage signal. PLL 600 further includes a low pass filter(LPF) 606 configured to receive the analog voltage signal. LPF 606 isconfigured to remove high frequency components of the analog voltagesignal and output a second control signal. PLL 600 further includes anoscillator circuit 608 configured to receive the second control signal.Oscillator circuit 608 is configured to output an output signal LO.Based on the second control signal, oscillator circuit 608 increases ordecreases a frequency of the output signal. PLL 600 further includes afeedback frequency divider (FD) 610 configured to receive the outputsignal. FD 610 is configured to generate feedback frequency f_(FBK),which is a multiple of reference frequency f_(REF).

Oscillator circuit 608 includes a varainductor. In some embodiments,oscillator circuit 608 includes varainductor 100 (FIG. 1), varainductor300 (FIG. 3), varainductor 400 (FIG. 4), or another suitablevarainductor. In some embodiments, oscillator circuit 608 has astructure similar to oscillator circuit 500 (FIG. 5). In someembodiments, the second control signal is the switch control signalVtune. In some embodiments, the second control signal is received byanother circuit configured to generate individual switch control signalsfor bit control of the varainductor similar to varainductor 300. In someembodiments, oscillator circuit is a VCO. In some embodiments,oscillator circuit 608 is a DCO.

In some embodiments where PLL 600 is included in a receiver device andoutput signal LO is mixed with a received signal prior to transmissionto external circuitry. In some embodiments, the received signal isamplified, e.g., by a low noise amplifier (LNA) prior to mixing with theoutput signal LO. The mixed output signal is transmitted to othercircuits within the receiver device.

FIG. 7 is a flow chart for method 700 of designing a varainductor inaccordance with one or more embodiments. In operation 702, an inductanceand a Q factor for the varainductor are selected. The inductance and Qfactor are determined based on a device into which the varainductor isincorporated. As a range of frequencies the device is configured toreceive increases, a higher Q factor is selected to enable initiation ofoscillation within the varainductor. Similarly, as the range offrequencies increases, a lower inductance of the varainductor isselected.

In operation 704, a width of a signal line, a width of a floating plane,a width of a ground plane, a length of a signal line and a spacingdistance between the signal line and the floating plane are determined.The parameters are determined based on the inductance and Q factor ofthe varainductor selected in operation 702. The relationship between thevarious parameters and the inductance and Q factor are described indetail above.

In operation 706, a number of switches between the floating plane andthe grounding plane is determined. The number of switches is determinedbased on a critical dimension of a manufacturing process used to formthe varainductor. In some embodiments, the number of switches is themaximum number of switches which can be formed along the length of thefloating plane based on the manufacturing process. As the number ofswitches increases, a tuning range of the varainductor increases;however, manufacturing of the varainductor becomes more complex andexpensive.

In operation 708, a spacing distance between the floating plane and theground plane is determined. The spacing distance between the floatingplane and the ground plane is determined based on the desired tuningrange during operation of the varainductor. As the spacing distanceincreases, the tuning range increases; however, an area of thevarainductor also increases.

FIG. 8 is a flow chart for a method 800 of operating a varainductor inaccordance with one or more embodiments. In operation 802, a signal linereceives an operating voltage. In some embodiments, the operatingvoltage is VDD.

In operation 804, an array of switches receives at least one switchcontrol signal. In some embodiments, each switch in the array ofswitches receives a same switch control signal. In some embodiments, atleast one switch in the array of switches receives a different switchcontrol signal from at least another switch in the array of switches. Insome embodiments, each switch receives a different switch control signalthan every other switch in the array of switches. In some embodiments,the switches of the array of switches are configured to close, i.e.,become electrically conductive, in response to a logically high signal.In some embodiments, the switches of the array of switches areconfigured to open, i.e. become electrically non-conductive, in responseto a logically low signal.

In some embodiments, the at least one switch control signal is thesecond control signal from LPF 606 (FIG. 6). In some embodiments, the atleast one switch control signal is a plurality of switch control signalsto enable bit control of the switch array. In some embodiments, theplurality of switch control signals is generated by an external circuitconfigured to receive the second control signal from LPF 606.

In operation 806, an inductance of the varainductor changes in responseto the at least one switch control signal. In some embodiments where anumber of closed switches increases in response to the at least oneswitch control signal, the inductance of the varainductor increases. Insome embodiments where a number of closed switches decreases in responseto the at least one switch control signal, the inductance of thevarainductor decreases. In some embodiments where the varainductor inpart of an oscillator circuit, an oscillation frequency of theoscillator circuit is configured to increase as the inductance of thevarainductor decreases. In some embodiments where the varainductor ispart of an oscillator circuit, the oscillation frequency of theoscillator circuit is configured to decrease as the inductance of thevarainductor increases.

FIG. 9 is a flow chart for a method 900 of operating a varainductor inaccordance with one or more embodiments. In operation 902, a PFDreceives a reference frequency. In operation 904, the PFD determines adifference between the reference frequency and a feedback frequency andgenerates a first control signal. In some embodiments, the first controlsignal indicates whether an oscillator circuit should increase ordecrease frequency oscillation.

In operation 906, a CP generates an analog voltage signal based on thefirst control signal.

In operation 908, a LPF removes high frequency components from theanalog voltage signal and outputs a second control signal.

In operation 910, an oscillator circuit receives the second controlsignal and at least one switch control signal and adjusts an oscillationfrequency of the oscillator circuit. The at least one switch controlsignal selectively connects a floating plane of a varainductor in theoscillator circuit to a ground plane of the varainductor. In someembodiments where a number of closed switches increases in response tothe at least one switch control signal, the inductance of thevarainductor increases and an oscillation frequency of the oscillatorcircuit decreases. In some embodiments where a number of closed switchesdecreases in response to the at least one switch control signal, theinductance of the varainductor decreases and the oscillation frequencyof the oscillator circuit increases. In some embodiments, the at leastone switch control signal is the second control signal from operation908. In some embodiments, the at least one switch control signal isgenerated by an additional controller circuit configured to receive thesecond control signal and output the at least one switch control signal.In some embodiments, the at least one switch control signal isconfigured to be a plurality of switch control signals for bit controlthe electrical connection between the floating plane and the groundplane.

In operation 912, a FD receives a portion of the output signal andgenerates the feedback frequency. The feedback frequency is received bythe PFD.

An aspect of this description relates to a varainductor. Thevarainductor includes a signal line over a substrate. The varainductorfurther includes a first ground plane over the substrate. Thevarainductor further includes a first floating plane over the substrate,wherein the first floating plane is between the first ground plane andthe signal line, and the first floating plane is a same distance fromthe substrate as the first ground plane. The varainductor furtherincludes a first transistor configured to selectively electricallyconnect the first ground plane to the first floating plane. Thevarainductor further includes a second transistor configured toselectively electrically connect the first ground plane to the firstfloating plane, wherein a gate of the first transistor is connected to agate of the second transistor. In some embodiments, the signal line is asame distance from the substrate as the first ground plane. In someembodiments, the varainductor further includes a shielding plane betweenthe signal line and the substrate. In some embodiments, the shieldingplane includes a plurality of slots. In some embodiments, the shieldingplane is free of slots. In some embodiments, the shielding plane iselectrically connected to the first floating plane. In some embodiments,the varainductor further includes a second floating plane over thesubstrate, wherein the signal line is between the first floating planeand the second floating plane, and the shielding plane is electricallyconnected to the second floating plane. In some embodiments, the secondfloating plane is a same distance from the substrate as the firstfloating plane. In some embodiments, the varainductor further includes asecond floating plane over the substrate, wherein the signal line isbetween the first floating plane and the second floating plane; a secondground plane over the substrate, wherein the second floating plane isbetween the signal line and the second ground plane; and a thirdtransistor, wherein the third transistor is configured to selectivelyelectrically connect the second ground plane to the second floatingplane.

An aspect of this description relates to a varainductor. Thevarainductor includes a signal line over a substrate. The varainductorfurther includes a first ground plane over the substrate. Thevarainductor further includes a first floating plane over the substrate,wherein the first floating plane is between the first ground plane andthe signal line, and the first floating plane is a same distance fromthe substrate as the first ground plane. The varainductor furtherincludes a first transistor configured to selectively electricallyconnect the first ground plane to the first floating plane. Thevarainductor further includes a second transistor configured toselectively electrically connect the first ground plane to the firstfloating plane, wherein a gate of the first transistor is electricallyseparated from a gate of the second transistor. In some embodiments, thegate of the first transistor is configured to receive a first controlsignal, and the gate of the second transistor is configured to receive asecond control signal different from the first control signal. In someembodiments, the varainductor further includes a third transistorconfigured to selectively electrically connect the first ground plane tothe first floating plane. In some embodiments, a gate of the thirdtransistor is configured to receive the first control signal. In someembodiments, a gate of the third transistor is configured to receive thesecond control signal. In some embodiments, a gate of the thirdtransistor is configured to receive a third control signal differentfrom the first control signal and the second control signal. In someembodiments, a voltage drop across the first transistor is differentfrom a voltage drop across the second transistor. In some embodiments,the signal line is a same distance from the substrate as the firstground plane.

An aspect of this description relates to a method of controllingvarainductor. The method includes receiving a voltage on a signal line.The method further includes receiving at least one control signal. Themethod further includes operating a plurality of switches in response tothe received at least one control signal, wherein operating theplurality of switches includes selectively electrically connecting afirst ground plane to a first floating plane, wherein the first floatingplane is between the first ground plane and the signal line, and thefirst floating plane is a same distance from a substrate as the firstground plane. In some embodiments, operating the plurality of switchesincludes operating all of the plurality of switches using a singlecontrol signal of the at least one control signal. In some embodiments,operating the plurality of switches includes operating a first switch ofthe plurality of switches using a first control signal of the at leastone control signal; and operating a second switch of the plurality ofswitches using a second control signal of the at least one controlsignal different from the first control signal.

It will be readily seen by one of ordinary skill in the art that thedisclosed embodiments fulfill one or more of the advantages set forthabove. After reading the foregoing specification, one of ordinary skillwill be able to affect various changes, substitutions of equivalents andvarious other embodiments as broadly disclosed herein. It is thereforeintended that the protection granted hereon be limited only by thedefinition contained in the appended claims and equivalents thereof.

What is claimed is:
 1. A varainductor comprising: a signal line over asubstrate; a first ground plane over the substrate; a first floatingplane over the substrate, wherein the first floating plane is betweenthe first ground plane and the signal line, and the first floating planeis a same distance from the substrate as the first ground plane; and afirst transistor configured to selectively electrically connect thefirst ground plane to the first floating plane; and a second transistorconfigured to selectively electrically connect the first ground plane tothe first floating plane, wherein a gate of the first transistor isconnected to a gate of the second transistor.
 2. The varainductor ofclaim 1, wherein the signal line is a same distance from the substrateas the first ground plane.
 3. The varainductor of claim 1, furthercomprising a shielding plane between the signal line and the substrate.4. The varainductor of claim 3, wherein the shielding plane comprises aplurality of slots.
 5. The varainductor of claim 3, wherein theshielding plane is free of slots.
 6. The varainductor of claim 3,wherein the shielding plane is electrically connected to the firstfloating plane.
 7. The varainductor of claim 6, further comprising asecond floating plane over the substrate, wherein the signal line isbetween the first floating plane and the second floating plane, and theshielding plane is electrically connected to the second floating plane.8. The varainductor of claim 7, wherein the second floating plane is asame distance from the substrate as the first floating plane.
 9. Thevarainductor of claim 1, further comprising: a second floating planeover the substrate, wherein the signal line is between the firstfloating plane and the second floating plane; a second ground plane overthe substrate, wherein the second floating plane is between the signalline and the second ground plane; and a third transistor, wherein thethird transistor is configured to selectively electrically connect thesecond ground plane to the second floating plane.
 10. A varainductorcomprising: a signal line over a substrate; a first ground plane overthe substrate; a first floating plane over the substrate, wherein thefirst floating plane is between the first ground plane and the signalline, and the first floating plane is a same distance from the substrateas the first ground plane; and a first transistor configured toselectively electrically connect the first ground plane to the firstfloating plane; and a second transistor configured to selectivelyelectrically connect the first ground plane to the first floating plane,wherein a gate of the first transistor is electrically separated from agate of the second transistor.
 11. The varainductor of claim 10, whereinthe gate of the first transistor is configured to receive a firstcontrol signal, and the gate of the second transistor is configured toreceive a second control signal different from the first control signal.12. The varainductor of claim 11, further comprising a third transistorconfigured to selectively electrically connect the first ground plane tothe first floating plane.
 13. The varainductor of claim 12, wherein agate of the third transistor is configured to receive the first controlsignal.
 14. The varainductor of claim 12, wherein a gate of the thirdtransistor is configured to receive the second control signal.
 15. Thevarainductor of claim 12, wherein a gate of the third transistor isconfigured to receive a third control signal different from the firstcontrol signal and the second control signal.
 16. The varainductor ofclaim 10, wherein a voltage drop across the first transistor isdifferent from a voltage drop across the second transistor.
 17. Thevarainductor of claim 10, wherein the signal line is a same distancefrom the substrate as the first ground plane.
 18. A method ofcontrolling varainductor comprising: receiving a voltage on a signalline; receiving at least one control signal; and operating a pluralityof switches in response to the received at least one control signal,wherein operating the plurality of switches comprises selectivelyelectrically connecting a first ground plane to a first floating plane,wherein the first floating plane is between the first ground plane andthe signal line, and the first floating plane is a same distance from asubstrate as the first ground plane.
 19. The method of claim 18, whereinoperating the plurality of switches comprises operating all of theplurality of switches using a single control signal of the at least onecontrol signal.
 20. The method of claim 18, wherein operating theplurality of switches comprises: operating a first switch of theplurality of switches using a first control signal of the at least onecontrol signal; and operating a second switch of the plurality ofswitches using a second control signal of the at least one controlsignal different from the first control signal.